With decreasing prices and increasing accuracy in pinpointing locations, Global Positioning System (GPS) devices such as GPS phones have become prevalent. As never before, voluminous GPS log data are accumulated continuously and unobtrusively. These large volumes of GPS data have given rise to a generation of conventional applications on the Internet (“the web”). Such applications allow users to upload, share, and browse GPS track logs. So far, however, GPS data have been utilized directly in relatively raw form without conventional applications providing much insight into the full potential GPS data can provide for tracking a person's experiences. Moreover, existing search methods that use tags, such as activity tags and region tags, do not generally satisfy users' needs to put the GPS data to full personal use.
Managing and understanding the collected GPS data are two important issues that could increase the value of the GPS data and the applications that use them. On one hand, indexing the ever-increasing GPS data could enable effective retrieval for users trying to find GPS data of interest. By understanding a user's GPS data, an application is more likely to provide novel services that will stimulate users to passionately contribute their GPS data. Thus far, however, GPS data are conventionally used in relatively raw form without much understanding of their full potential.